How to clean the HDD from the old system, leaving only the necessary?

Question

macOS

Mac Book Pro MID 2012.
The old HDD has been moved to the place of the DVD, the new SSD has taken its regular place.
A fresh system is installed on the SSD. A copy of the system was previously made using Time Machine. I would like to clean the HDD from the old system, leaving only the necessary files.
Question: How to clean the HDD from the old system, leaving only the necessary? Can this be done using Time Machine, or is it better to just copy the necessary documents to external media in advance?

Answer 1

Of course, it's better to just copy the necessary documents.
And in general, if all the necessary documents are not located anywhere, but in folders strictly known to you, this is categorically convenient - in the case of a backup copy, moving to another laptop, reinstallation - you know that these 5 folders are copied and that's it.
But this is a question of more than one's own organization.

Answer 2

Just manually delete what you don't need.